Myoglobin as a conservation-relevant predictor of short-distance flight capacity in Neotropical forest birds

Some forest-dwelling tropical bird species are unable or unwilling to fly even a few hundred meters across habitat discontinuities, restricting connectivity of isolated populations in fragmented landscapes. Experimental evidence for flight limitation has reliably predicted occurrence across archipelagoes of habitat fragments varying in their distance from potential source populations. Mechanistic explanations for large differences in flight capacity of tropical birds, even over remarkably short distances, have not been tested. We evaluated myoglobin concentration in pectoralis muscles and hearts of eight Neotropical species for which experimental evidence revealing a wide range of flight abilities exists. We found a strong positive relationship between myoglobin concentration in the pectoralis muscles, but not hearts, and average over-water flight distance during dispersal-challenge experiments. The approximately 2.5-fold difference in pectoralis myoglobin concentration is directly associated with flight capacity and allows predictions of species or species groups most likely to be impeded by habitat discontinuities and therefore at conservation risk in fragmented landscapes.